The present invention concerns an improved method for adhering brass and brass-plated metal to rubber. It also concerns a new class of rubber compounds having improved adhesion characteristics to brass-plated metal.
The problem of securing adequate adhesion of rubber to metal has been investigated extensively by those skilled in the various aspects of rubber manufacturing. The best known reference on this subject, Buchan, Rubber Metal Bonding (Crosby, Lockwood & Son, London, 1948) describes the now widespread practice of vulcanization of rubber onto a brass-plated metal substrate. The use of bonding agents such as isocyanates, rubber halogens, and thermoplastics, between the metal and the rubber is found in some applications.
The alteration of the rubber compound itself to improve its adhesion to the metal substrate has been considered, and one such alteration is disclosed in Canadian Pat. No. 793,794. An acidic compound and a free radical curing system is incorporated into rubbers and rubbery copolymers under the teachings of the Canadian patent.
Compounds of various rubbers, natural and synthetic, with small amounts of certain polymeric polysulfides, are described in British Pat. No. 1,144,634. Advantages taught in the British patent are reduced sulfur requirement, ease of compounding, and nonblooming vulcanizates.
The adhesion of polysulfides to metals (aircraft fuel tanks) is mentioned in U.S. Pat. No. 3,099,643, and their use as a cold setting adhesive for glass, wood and metals is discussed in Jorczak and Fettes, "Polysulfide Liquid Polymers," Industrial and Engineering Chemistry, Vol. 43, pp. 324, 327 (February, 1951).